This section provides background information related to the present disclosure which is not necessarily prior art.
FIG. 1 illustrates one exemplary embodiment of the semiconductor light emitting device disclosed in U.S. Pat. No. 7,262,436. The semiconductor light emitting device includes a substrate 100, an n-type semiconductor layer 300 grown on the substrate 100, an active layer 400 grown on the n-type semiconductor layer 300, a p-type semiconductor layer 500 grown on the active layer 400, electrodes 901, 902 and 903 formed on the p-type semiconductor layer 500, with the electrodes serving as reflective films, and an n-side bonding pad 800 formed on the n-type semiconductor layer 300 which had been etched and exposed.
A chip having the above structure, i.e. a chip where all of the electrodes 901, 902 and 903, and the electrode 800 are formed on one side of the substrate 100, with the electrodes 901, 902 and 903 serving as reflective films, is called a flip chip. The electrodes 901, 902 and 903 are made up of an electrode 901 (e.g. Ag) having a high reflectance, an electrode 903 (e.g. Au) for bonding, and an electrode 902 (e.g. Ni) for preventing diffusion between the material of the electrode 901 and the material of the electrode 903. While the benefits of such a metal reflective film structure are a high reflectance and effectiveness for current spreading, a possible drawback thereof is light absorption by the metal.
FIG. 2 illustrates an exemplary embodiment of the semiconductor light emitting device disclosed in JP Laid-Open Pub. No. 2006-20913. The semiconductor light emitting device includes a substrate 100, a buffer layer grown on the substrate 100, an n-type semiconductor layer 300 grown on the buffer layer 200, an active layer 400 grown on the n-type semiconductor layer 300, a p-type semiconductor layer 500 grown on the active layer 400, a light transmitting conductive film 600 with a current spreading function, which is formed on the p-type semiconductor layer 500, a p-side bonding pad 700 formed on the light transmitting conductive film 600, and an n-side bonding pad 800 formed on the n-type semiconductor layer 300 which had been etched and exposed. Further, a DBR (Distributed Bragg Reflector) 900 and a metal reflective film 904 are provided on the light transmitting conductive film 600. While this structure shows reduced light absorption by the metal reflective film 904, a possible drawback thereof is that current spreading is not smooth, as compared with the structure with the electrodes 901, 902 and 903.
FIG. 11 illustrates an exemplary embodiment of a conventional Group III-nitride semiconductor light emitting device. The Group III-nitride semiconductor light emitting device includes a substrate 10, a buffer layer 20 grown on the substrate 10, an n-type Group III-nitride semiconductor layer 30 grown on the buffer layer 20, an active layer 40 grown on the n-type Group III-nitride semiconductor layer 30, a p-type Group III-nitride semiconductor layer 50 grown on the active layer 40, a p-side electrode 60 formed on the p-type Group III-nitride semiconductor layer 50, a p-side electrode pad 70 formed on the p-side electrode 60, an n-side electrode 80 formed on an exposed portion of the n-type Group III-nitride semiconductor layer 30 created by mesa etching the p-type Group III-nitride semiconductor layer 50 and the active layer 40, and a protective film 90.
The substrate 10 may be a homogeneous substrate, such as a GaN-based substrate, or a heterogeneous substrate, such as a sapphire substrate, a SiC substrate or a Si substrate, but any type of the substrate is acceptable as long as a Group III nitride semiconductor layer can be grown thereon. When a SiC substrate is use, the n-side electrode 80 may be formed on the SiC substrate.
FIG. 12 illustrates an exemplary conventional method for mounting a semiconductor light emitting device on a frame 5, in which an adhesive 9 such as the Ag paste is used to bond the semiconductor light emitting device onto the frame 5. A part of the light generated by the active layer 40 is emitted directly through the light-transmitting p-side electrode 60, and another part of the light that had entered the substrate 10 is reflected from an Al layer 92 to be emitted through the lateral face of the light emitting device or the p-side electrode 60. Despite the high reflectance of the Al layer 92, a portion of the light is still absorbed by the Al layer. When the adhesive 9 used is a clear paste in the absence of the Al layer 92, the light transmits through the adhesive and is reflected from the frame 5. Again, the frame 92 can also absorb the light, resulting in a light loss, and the clear paste having a low thermal conductivity is not suitable for high-current operations. As the semiconductor light emitting device is usually a very thin compound semiconductor light emitting device and it slightly sticks out along the side of the substrate 10 while the light emitting device is being bonded to the frame 5 by means of an adhesive provided on the frame, a part of the light entering the substrate can be absorbed by the adhesive 9. Even when the adhesive 9 used is a clear paste, it still absorbs varying levels of light. Hence, an amount of the light emitting from the light emitting device is reduced, thereby lowering light extraction efficiency of the light emitting device.
FIG. 13 illustrates an exemplary conventional Group III-nitride semiconductor light emitting device 201, which includes lead frames 210, 220, a mold 230, an encapsulant 240, a Group III-nitride semiconductor light emitting device chip 250, and a Zener diode 260 for ESD protection. The Group III-nitride semiconductor light emitting device chip 250 is placed on the lead frame 210 and electrically connected to the lead frame 210 and the lead frame 280 by means of a wire 270 and a wire 280, respectively. The Zener diode 260 for ESD protection is placed on the lead frame 220, with it being electrically conductive therewith, and is also electrically connected to the lead frame 210 by means of a wire 290.
FIG. 14 illustrates an exemplary vertical light emitting device. Similar to one shown in FIG. 11, this vertical light emitting device includes an n-type Group-Ill nitride semiconductor layer 300, an active layer 400, a p-type Group-Ill nitride semiconductor layer 500, a p-side electrode 600 and a p-side bonding pad 700, in the order mentioned. A substrate 100 is removed once those three layers 300, 400 and 500 are grown, and an n-side electrode 800 is then formed on the other side of the n-side Group III-nitride semiconductor layer 300. The vertical light emitting device is configured to facilitate smoother current spreading, as compared with the light emitting device shown in FIG. 11.
FIG. 26 illustrates an exemplary process of manufacturing a semiconductor light emitting device. In a packaging process, semiconductor light emitting chips 101 are die-bonded onto a lead frame with a die bonder. Subsequently, processes including wire-bonding, phosphor encapsulation, property testing, trimming, taping and the like are carried out to obtain a semiconductor light emitting device package. In this process, a sorter 501 is used, as shown in FIG. 26a, to hold and carry a semiconductor light emitting chip 101 onto a tape 13 by electrical suction or vacuum suction. At this time, an ejection needle 802 strikes the semiconductor light emitting chip 101 to facilitate the release of the semiconductor light emitting chip 101 from the tape 13. The ejection needle 802 as shown in FIG. 26b has a diameter of 50 μm to 80 μm, but it may vary depending on a desired form or area of the semiconductor light emitting chip. The ejection needle 802 sometimes collides with a microscale structure like a finger electrode for current spreading, which may be present in the semiconductor light emitting chip 101, and causes possible defects such as a crack or short in the finger electrode.
FIG. 38 illustrates an exemplary conventional Group III-nitride semiconductor light emitting device. The Group III-nitride semiconductor light emitting device includes a substrate 10 (e.g. sapphire substrate), a buffer layer 20 grown on the substrate 10, an n-type Group III-nitride semiconductor layer 30 grown on the buffer layer 20, an active layer 40 grown on the n-type Group III-nitride semiconductor layer 30, a p-type Group III-nitride semiconductor layer 50 grown on the active layer, a current spreading conductive film 60 formed on the p-type Group III-nitride semiconductor layer 50, a p-side bonding pad 70 formed on the current spreading conductive film 60, an n-side bonding pad 80 formed on an exposed portion of the n-type Group III-nitride semiconductor layer 30 created by mesa etching the p-type Group III-nitride semiconductor layer 50 and the active layer 40, and a protective film 90.